"May, 2013"

Includes bibliographical references (pages 37-49)

Introduction -- Scope -- Background: Prairie Pothole Wetlands and Intermittent/Ephemeral Streams -- Methods -- Results -- Discussion -- References -- Appendix A. Approximate crosswalk between classification schemes -- Appendix B. Keywords and search used in database searches -- Appendix C: Faunal species associated with PPR wetland and streams -- Appendix D: Number of sources describing ecological change in wetland function following hydrologic alterations

Numerous published and unpublished studies have examined the relationship between wetland hydrology, wetland processes and functions, and wetland-dependent biota. The goal of the present project was to review existing studies, models, and local expert knowledge to describe hydrology-ecology relations under natural conditions and to generate a systematic characterization of the relationships between hydrologic regimes and biological dependencies of prairie wetlands in Montana. This report describes the scope of the project, provides some of the background information used to frame the literature review, summarizes the methods, and presents and discusses the findings of the review. The projects broad geographic scope was defined as the Prairie Pothole Region (PPR) of North America, which extends across approximately 715,000 km of five US states (Iowa, Minnesota, North Dakota, South Dakota and Montana) and three Canadian provinces (Manitoba, Saskatchewan and Alberta). Within that area, it focuses on the 95,907 km Northwestern Glaciated Plains ecoregion of Montana. The topical scope of the project is the pothole wetlands of the PPR, and the intermittent and ephemeral streams present in the region. Because the wetlands of the PPR are so important to North American waterfowl and other migratory birds, the area has attracted substantial research interest. Scientific investigations have been far-ranging, from basin-specific short term studies of specific species and wetland components to long-range, landscape-level analyses and models. Over the years, this has resulted in a more complete, and more nuanced, understanding of ecosystem processes and functions and a better characterization of the inherent variability of the region. In this report, we begin by describing the Prairie Pothole Region (PPR) and the wetlands and streams that characterize it. We then discuss the methods we used to search for, summarize, and interpret research reports, agency documents, expert knowledge and models. The extreme variability of wetland and stream habitats in the PPR accounts for much of its diversity. In our Results section, we examine how differences between natural and human hydrologic change affect the functions, processes and biota that depend on wetlands and streams, and how this affects regional diversity. This is followed by a summary of the impact of anthropogenic change on a common suite of wetland and stream, notably 1) flood mitigation; 2) water storage and streamflow maintenance; 3) groundwater recharge; 4) sediment retention; 5) nutrient and chemical cycling; 6) plant community maintenance; and 7)maintenance of faunal habitat and biodiversity. In sum, we review over 150 published sources. We conclude that ecological responses to natural changes in wetland hydrology are variable, depending on the direction of change and the species, guild or function affected. For example, droughts generally lead to decreases in avian, macroinvertebrate and fish abundance, depending on the extent and duration of the drought. Flood cycles, in contrast, promote both greater abundance and changes in community structure. However, ecological responses to anthropogenic alteration are almost entirely negative. This difference reflects the duration of natural vs. anthropogenic change. Natural hydroperiods of wetlands and prairie streams vary spatially and temporally, with flood and drought cycles altering. In contrast, human manipulations of flood frequency, duration or extent tend to be permanent, as are the changes in wetland function that they induce. The Discussion section sets forth some of the implications of these conclusions, and lays out directions for future research. The Bibliography and Appendices provide more detail about our sources and approach

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